Greetings: There is so much good stuff on RF Cafe that there is no way to list or link to
all of it here. Please use the Search box or the Site Map
to find what you want - there is a good chance I have it. Thanks!

PLL's an more important Low pass folter - RF Cafe Forums

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would
be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate
that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views.
It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if
you would like to post something on RF Cafe's
Facebook page, please do.

Joined:
Wed Sep 15, 2004 3:15 amPosts: 4Location: Huntington beach
Well first i would like to know if anyone knows any online places
that have goos info on pll's? searching i only came up woth some very
basic stuff like wkipedia. But my main question is on the after
the phase comparator the lpf (can this be a band pass?) and how exactly
does it effect settleing time. I would think a narrower bandiwidth will
lock loop faster since it would pass less noise. And i thought that
the filters job was just to pass dc because thats what input to the
varactor on the vco?

Sorry for the "newb" question but i actually
never seen a pll circuit, we use it internal to the chip so i cant probe
around.

Joined: Mon
Jun 27, 2005 2:02 pmPosts: 373Location: Germany The only
filter possible in PLL is a LPF. The purpose of the LPF is to smooth
the output of the FPD (Frequency Phase Detector) and it sets the speed
of the loop.

A wide filter will cause the loop to react faster,
since the filter's pole(s) is/are located far, therefore, the filter
has a wider reponse. The tradeoff, as you mentioned, will be a degradation
in phase noise and vice versa.

Top

electrodummie
Post subject: Posted: Thu Aug 16, 2007 4:33 pm

Lieutenant

Joined: Wed Sep 15, 2004 3:15 amPosts: 4Location: Huntington
beach Thanks. i had not had the chance to thank you guys been doing
alot of reading. I do understand pll better but not enough yet.